1. Field of the Invention
The present invention relates to an XY table for a semiconductor manufacturing apparatus and more particularly to a structure for such an XY table that is controlled with high precision.
2. Prior Art
In a wire bonding apparatus and other semiconductor manufacturing apparatus, an XY table is employed so as to move the semiconductor device and other object to be processed in two directions (that is, in an X axis direction and a Y axis direction) that are perpendicular to each other on a horizontal plane.
As semiconductor elements have become increasingly integrated in recent years, the operating precision demanded to an XY table has reached the sub-micron level. As a result, various methods have been proposed for suppressing the vibration of the XY table and for positioning the table more precisely.
For instance, Japanese Patent No. 2,981,999 proposed by the present applicant discloses a method for canceling out reaction force in the operation of a reciprocating linear motor (hereinafter called xe2x80x9cmotorxe2x80x9d) that drives an XY table. In this structure, the motor main body is supported so that it can move in the opposite direction from the drive body; as a result, reaction force when a drive body is driven is canceled out.
Unfortunately, when a prototype was built in which this motor was installed in an XY table with a commonly used structure, control became unstable as resolution was increased, and the desired positioning precision could not be obtained.
This problem was further scrutinized, and it was revealed that the cause of the problem was not the vibration of the motor, but the structure of the conventional XY table to which the motor was applied.
More specifically, in the conventional XY table shown in FIG. 5, a lower table 60X directly coupled to an X movable element 58X of an X motor 51X that drives in the X axis direction is supported movably in the X axis direction and immovably in the Y axis direction on a table support block 62. In addition, an upper table 60Y is supported movably in the Y axis direction by a guide rail 61Y over the lower table 60X, and a Y movable element 58Y of a Y motor 51Y that drives in the Y axis direction is connected to this upper table 60Y via a guide 73 that is comprised of a roller 71 and a slider 72 and has freedom in the X axis direction. However, play in this guide 73 reduces the positioning precision.
Furthermore, in a configuration in which the upper table 60Y is offset from the Y movable element 58Y of the Y motor 51Y (that is, a configuration in which the Yxe2x80x94Y line (the center line of the weight distribution of the Y movable element 58Y) does not coincide with the center line TC of the weight distribution of the upper table 60Y), operation of the Y motor 51Y causes a thrust F in the yaw direction to act upon the upper table 60Y. As a result, wear and play in the sliding portion of the guide rail 61Y adversely affects positioning, causing control instability and a decrease in positioning precision.
Accordingly, the object of the present invention that is conceived on the basis of above-described new finding is to provide an XY table that has a higher positioning precision with an improved structure.
The above object is accomplished by a unique structure of the present invention for an XY table for a semiconductor manufacturing apparatus, in which a first drive unit (X motor) for driving a first drive body (X movable element) in a first direction (X direction) by means of a first motor main body (X motor main body) and a second drive unit (Y motor) for driving a second drive body (Y movable element) in a second direction (Y direction) by means of a second motor main body (Y motor main body) are disposed so that the first and second direction intersect at right angles, wherein the XY table is comprised of:
a lower table (X table) fixed to the first drive body (X movable element), and
an upper table (Y table) fixed to the second drive body (Y movable element); and further
the upper table (Y table) is supported movably in the second direction (Y direction) and immovably in the first direction (X direction) on the lower table (X table),
the first drive body (X movable element) is immovable in the second direction (Y direction) with respect to the first motor main body (X motor main body),
the second drive body (Y movable element) is movable in the first direction (X direction) with respect to the second motor main body (Y motor main body), and
the second motor main body (Y motor main body) is provided with a magnetic field forming means (permanent magnet)) that covers an entire region of movement of a magnetic action component of the second drive body (Y movable element) in the first direction (X direction).
In this structure, the lower table (X table) and upper table (Y table) are fixed to the first drive body (X movable element) and second drive body (Y movable element), respectively. Accordingly, it is possible to prevent precision decrease that is seen in the conventional XY table caused by play in the guide member (the guide 73). Also, the first drive body (X movable element) is provided so as to be immovable in the second direction (Y direction) with respect to the first motor main body (X motor main body). Accordingly, even when the upper table (Y table) or what it carries is very heavy, any misalignment of the lower table (X table) in the second direction (Y direction) that would otherwise be caused by friction between the two tables can be prevented. Furthermore, the magnetic action of the second motor main body (Y motor main body) on the second drive body (Y movable element) remains constant regardless of the position of the second drive body (Y movable element) in the first direction (X direction). Thus, the upper table (Y table) is subjected to no thrust in the yaw direction, and therefore an increase in wear or play of the guide member (guide rail 61Y) for guiding the upper table (Y table) in its movement direction can be suppressed, misalignment and rotational vibration are less likely to occur, and high-precision and stable positioning can be performed.
In the present invention, the above XY table can further include a position sensor that is disposed on an symmetry axis of thrust in a second movable component that is comprised of the second drive body (Y movable element) and the upper table (Y table).
In this structure, the effect that misalignment of the second drive body (Y movable element) in the yaw direction has on the detection value of the position sensor can be minimized, affording greater detection precision.
The above-described position sensor can be disposed on the symmetry axis of thrust in a first movable component that is comprised of the first drive body (X movable element) and the lower table (X table).
Accordingly, the effect that misalignment of the first drive body (X movable element) in the yaw direction has on the detection value of the position sensor can be minimized.
Furthermore, in the XY table of the present invention, a reaction force produced by driving the first drive body (X movable element) and second drive body (Y movable element) is set so as to be canceled out by way of:
providing the first motor main body (X motor main body) to be movable in an opposite direction from the first drive body (X movable element) when the first drive body (X movable element) is driven, and
providing the second motor main body (Y motor main body) so as to be movable in an opposite direction from the second drive body (Y movable element) when the second drive body (Y movable element) is driven.
With this structure, vibrations can be minimized, and an even higher detection precision is obtained.